Moesin, which stands for membrane-organizing extension spike protein, is a membrane bound intracellular protein initially indentified in bovine uterus and characterized as a possible receptor for heparin. Lankes et al., Biochem J. 251:831-42 (1988). Full length native human moesin has 577 amino acids, with a molecular weight of about 75 kD. It shares about 98.3% sequence identity with mouse moesin. Sato et al., J. Cell Sci. 103:131-143 (1992).
Further studies have characterized moesin as a member of the ezrin-radixin-moesin (ERM) protein family. These are proteins that are primarily expressed in cytoplasm, concentrated in actin rich cell-surface structures. Sequence and structural analysis of the ERM proteins revealed that they share high degrees of inter-species and inter-molecular homologies. The ERM proteins have three domains: an N-terminal domain called FERM domain (band four-point-one, ezrin, radixin, moesin homology domain) because of its homology with the band 4.1 protein, a central helical domain and a C-terminal tail domain. The C-terminal tail domain binds F-actin while the N-terminal FERM domain is responsible for binding to adhesion molecules in the plasma membrane. Louvet-Vallee (2000).
The functions of ERM proteins are regulated by an intramolecular interaction between the N-terminal FERM domain and the C-terminal tail domain. Pearson et al., Cell 101:259-70 (2000); Louvet-Vallee (2000). The ERM proteins exist in two states in terms of activities: a dormant state and an active state. The active form is involved in intercellular interactions and the dormant form is present in cytoplasm. The difference between these two states depends on the conformation of the protein. In dormant form, the FERM domain is tightly bound to the tail domain, mutually masking the binding sites for other molecules on each domain. The central helical domain serves as a flexible bend to enable the reach and binding of the two terminal domains. Dormant moesin becomes activated when the tightly bound structure opens up, with the FERM domain attaching to the membrane by binding specific membrane proteins and the last 34 residues of the C-terminal tail domain binding to actin filaments.
Within the tail domain, there exists a threonine residue at position 558 of moesin (Thr 558) (position 564 for radixin and 567 for ezrin), whose phosphorylation has been shown to play a key role in the activation of ERM proteins. Pearson et al. (2000). Phosphorylation at Thr 558 weakens the FERM/tail interaction and, in the presence of phospholipids, unmasks the membrane protein and F-actin binding sites on relative domains. In addition, the activated FERM domain also participates in the Rho signaling pathway. Takahashi et al., J. Biol. Chem. 272:23371-5 (1997). In moesin, Thr 558 is believed to be phosphorylated by a rho associated coiled coil forming protein kinase (ROCK). Oshiro et al. J. Biol. Chem. 273:34663-6 (1998). Other protein kinases known to cause Thr 558 phosphorylation include, but not limited to, PKC, PIP5KIa, P38 and Slik. Hipfner et al., Genes Dev. 18:2243-8 (2004).
The presence and functions of moesin and other ERM proteins have been implicated in many physiological as well as pathological conditions. They act as structural linkers between the plasma membrane and the actin cytoskeleton, playing roles in the formation of microvilli, cell-cell adhesion, maintenance of cell shape, cell mobility and membrane trafficking. Later studies have revealed that they are also involved in many signaling pathways including Rho pathway, PI3-kinase/Akt pathway and CD14 pathway. Louvet-Vallee, Biol. Cell 92:305-16 (2000); Thome et al., Infect. Immun. 67:3215 (1999). Moesin has been suggested to play roles in the growth and metastasis of certain cancers.
Moesin has also been associated with autoimmune diseases. Wagatsuma et al reported detections of anti-ERM autoantibodies in patients with rheumatoid arthritis (RA). Wagatsuma et al., Mol. Immunol. 33:1171-6 (1996). Of the 71 patient sera tested, 24 samples (33.8%) reacted with at least one of the recombinant ERM antigens and 10 samples (14%) reacted with recombinant moesin alone. However, the study did not find significant correlation between the presence of anti-ERM antibodies and clinical manifestation, such as disease duration or stage. Moreover, sera from patients with other autoimmune diseases such as Primary Sojgren's Syndrome (PSS) and systemic lupus erythematosus (SLE) did not show any reactivity to the three ERM proteins.
Takamatsu et al reported detection of specific antibodies to moesin in the sera of patients with acquired aplastic anemia (AA). Takamatsu et al., Blood 109:2514-20 (2007). Using ELISA, anti-moesin antibodies were shown at high titers in 25 of 67 (37%) AA patients. Further in vitro studies showed that anti-moesin antibodies from AA patients induced inflammatory cytokines such as TNF-α and IFN-γ, implicating its role in the pathophysiology of the disease. Espinoza et al., Intl. Immu. 21:913-23 (2009); Takamatsu et al., J. Immunol. 182:703 (2009).
Given the complex and important functions of human moesin protein in multiple physiological and pathological settings, it is desirable to explore clinically relevant molecular entities capable of modulating moesin activities, as well as methods of making and using the same. The present application described herein provides these and other benefits.
All references cited herein, including patent applications and publications, are incorporated by reference in their entirety.